Phil Howard's Pico Listens for Telnet Connections — Giving You a Direct Line to Leave Him a Message

Connected to, and powered by, a compact router, this Pico acts as a simple messaging terminal accessible to all via the Internet.

Maker and Pimoroni software lead Phil Howard has connected a Raspberry Pi Pico to the web as an anonymous messaging terminal, allowing anyone to pen their thoughts on an attached display.

The low-cost Raspberry Pi Pico, the first outing for the company's in-house RP2040 microcontroller, is proving a very popular device. While it includes a range of smart features like its programmable input/output (PIO) blocks, it doesn't offer a means of connecting to a network — which is where Howard's project comes in.

"So I have the GL.iNet AR300M [router] powering a Raspberry Pi Pico and bridging its serial terminal — via ser2cat — to my local network," Howard writes of the project. "Can I go one better and bridge that to WAN [Wide Area Network]?"

The answer, it turns out, is yes. The next step: Having it do something useful, and exposing it to the world as a whole.

"I made a thing," Howard revealed, showing the final build: A device which accepts connections over the Telnet protocol, waits for messages to be typed — then displays them in a retro green typeface on an attached display.

"It stores everything as a std::string in memory and never cleans up/truncates the scrollback explicitly," Howard notes, "so eventually the Pico will run out of RAM and the whole thing will die. I guess technically I could peek at the contents with the debugger."

"I guess I should install something on it like FORTH, or some kind of text adventure port."

Those interested in trying it out can use the Telnet client of their choice to connect to on port 40721.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire:
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